The present invention relates to an oil-injectiontype rotary compressor. At present, widely employed are such compressors of the slide vane type, the screw type, the worm type and the like in which cooling and lubricating oil is directly injected into the compressed gas in order to enhance the cooling effect and to obtain the higher compression efficiency of the compressor. Moreover, the machinery of these types is, as compared with any conventional one of the reciprocating type, featured in that it will cause remarkably less public nuisances and troubles such as vibration, noise and the like, and therefore it is outstandingly superior thereto.
However, the oil-injection-type rotary compressor in which cooling and lubricating oil is directly injected into the compressed gas is endowed with its only one defect that it is frequently suffered from such a trouble that, during its operation with highly humid suction gas, the sucked water vapour contained therein is reached to its dew point in relation to the temperature thereof, and thus condensed water particles are mixed with the cooling and lubricating oil so as to allow the oil to become emulsified.
In the case where the ambient air is sucked into the oil-injection-type rotary compressor to get compressed, if the ambient air to be sucked is highly heated and humid, the dew point of the vapour is elevated as the compression pressure is increased, and even though both the temperatures of the cooling and lubricating oil itself and of that contained in the compressed air circulating system are very high, the water vapour is condensed to form a lot of water drops suspended in the cooling and lubricating oil, and the oil and water drops are agitated and combined into mineral particles mixing with each other, in the compression chamber of the compressor and in the oil pump for the compressor, until the mixed oil water particles are entirely converted to a colloidal phase so as to form a kind of petroleum emulsion, thus resulting in that the oiliness is lost and failure of the compressor is possibly caused thereby. In addition, a phenol resin vane used in slide-vane type compressor and phenol resin pinion used in worm type compressor absorb the water particles contained in lubricating oil and is expanded, resulting in that the compressing function of the vane is impaired, or otherwise, the vane and pinion might be broken down.
Heretofore, a generally adopted method to prevent emulsification as described above was such that the temperature of the cooling and lubricating oil supplied to the compressor was maintained above a definite temperature while the compressor was operated, and the water vapour contained in the sucked air was discharged, in the form of vapour as it had been, out of a discharge port of the compressor.
Therefore, the temperature of the cooling and lubricating oil could not be lowered below a definite temperature and was kept at a higher temperature at which the lubricating oil was quickly oxidized so as to accelerate the deterioration of the lubricating oil, resulting in such a short effective life of the oil as 1,000 hours at most. Furthermore, the suction efficiency of the atmospheric air sucked into the compressor was also impaired due to its high temperature involved by a higher level of the temperature of the cooling and lubricating oil, said level being required as the temperature of the oil supplied to the compressor.
Moreover, for the purpose of maintaining the operating temperature of the cooling and lubricating oil above the definite temperature level, even if the temperature of the oil is regulated by means of a temperature regulating device, i.e., an element such as a so-called thermostat, in such a case where the amount of the compressed air being put to use at its discharging side is extremely limited to only a little, the heat energy generated by the compression is remarkably decreased so that it is difficult to keep both the temperature of the discharged air and the temperature of the lubricating oil to respective appropriate levels, consequently, condensed water particles are increasingly contained in and mixed with the cooling and lubricating oil within its circulating system. Therefore, it was a customary practice to discharge, at least once a day, the gathered water in a lubricating oil reservoir by opening a drain cock at the bottom of the reservoir when the temperature of the cooling and lubricating oil in the reservoir has lowered down after the operation of the compressor was interrupted or terminated.
However, this method cannot be put into a practical use in such a case where the compressor are operated continuously for many day on the basis of a complete 24 hours daily operation, and therefore the cooling and lubricating oil would be soon deteriorated inevitably.
Recently, requirements for the 24 hours continuous work lasting for great many weeks to meet the work with a high pressure and to carry out the continuous non-attendant operation are frequently called for, therefore if the contaminated water particles in the cooling and lubricating oil are not automatically separated and discharged therefrom during the operation, whatsoever the oil injection type rotary compressor may be superior in its performance, and there may occur a least public nuisance and trouble such as vibration, noise and the like, it will not be reliable and may be discontinued to be used in some cases.
The object of the present invention is to provide an oil-injection-type rotary compressor in which the suction efficiency of the compressor is improved and the deterioration of the cooling and lubricating oil due to oxidation thereof is prevented by lowering the temperature of the cooling and lubricating oil which is being supplied to the compressor, in addition, the water particles mixed with the cooling and lubricating oil are automatically removed therefrom either continuously or intermittently and discharged to the exterior thereof by means of a centrifugal water separator inserted in the path of the cooling and lubricating oil, whereby, the effective life of the cooling and lubricating oil is extended over 10,000 hours and it is also made possible to operate the compressor continuously for a long period of many weeks.
On the other hand, in an oil-injection-type rotary compressor of a high pressure, as the dew point under the high pressure becomes higher than the oxidation temperature for the cooling and lubricating oil, the emulsifying function for the cooling and lubricating oil is accelerated remarkbly in response thereto. Therefore, it has been found that the oil injection type rotary compressor can not be put in use under such a high pressure. But, according to the present invention, this problem is also solved so that the range of the available pressures of the oil injection type rotary compressor can be further extended.
It is in general told that water and oil are hard to be mixed with each other, but actually, water and oil are easily and well mixed to make up a mixture thereof. When water is merely added into oil, the water is kept completely separated from the oil, however, if they are either agitated violently or broken into mineral particles by passing them through a gear pump, the oil and water are fully mixed together to change into a turbid white emulsion and if this state of emulsion is once made up, although anybody tries to separate oil from water by any means, he will never succeed therein under the ambient temperature.
Now, it was found by our experiments that even the oil and water mixed to form an emulsified phase can be separated gradually in response to its temperature elevated higher than the normal temperature. In the passage of the cooling and lubricating oil having a high temperature before the time when the cooling and lubricating oil was cooled by a cooler, was inserted a centrifugal water separator, by means of which it has become possible to completely separate oil from the mixed water.
As a result of various experiments, in separating emulsified water in cooling and lubricating oil by centrifugal separator, it is found that oil and water are different in the rate of variation of viscosity to that of temperature and in the rate of variation of surface tension to that of temperature so that it is difficult to separate them from each other and that it is possible to separate them by means of elevation of temperature of oil, and if suitable peripheral speed is given to the centrifugal separator corresponding to the temperature of oil and water, it is possible to separate oil from water with ease. Namely, it is found that if periperhal speed N m/sec of the centrifugal separator and oil temperature T.degree.C are defined within the range where the upper limit is expressed by ##EQU1## and the lower limit is expressed by EQU 0.049 N.sup.2 + 0.605 N + T = 55
oil and water can be perfectly and easily separated from each other under any condition.